The present invention relates a method of and an apparatus for cleaning a plurality of paint spray guns by placing the paint spray guns in a cleaning tank with a plurality of cleaning nozzles disposed therein, and ejecting a solvent such as a thinner from the cleaning nozzles to clean the paint spray guns and the interiors of pipes which supply paint to the paint spray guns, for thereby cleaning the paint spray guns efficiently and automatically within a short period of time so that the painting process is easily automatized.
Automobile industry generally employs a painting apparatus for applying paint coating to the outer panels of automobile bodies. The painting apparatus is automatized in order to meet the assembling process of a line production system. In general, the painting apparatus comprises a plurality of paint spray guns. While the paint spra guns and an automobile body to be painted are being relatively moved, paint is sprayed from the paint spray guns to automatically apply a paint coat on the automobile body.
As paint of one color is coated on successive automobile bodies, the paint which is ejected from one paint spray gun is apt to be deposited on the tip end or nozzle of the paint spray gun. When a paint coat of another color is subsequently applied from the same paint spray gun, the deposited paint on the nozzle of that paint spray gun mixes or chemically reacts with the ejected paint, and the paint mixture or reaction product is solidified and cloggs the nozzle, with the result that paint may not be sprayed from the paint spray gun in a subsequent paint spraying process.
Heretofore, it has been customary, before and after a painting process is carried out, for the worker to wash the nozzles of paint spray guns with a solvent such as a thinner applied to a brush and then wipe any solvent off the nozzles with a piece of cloth thereby to clean the paint spray guns.
Since the paint spray guns are manually cleaned by the worker, the cleaning process is quite timeconsuming and imposes a heavy burden on the worker especially when cleaning an automatic painting apparatus having many paint spray guns. Intervention by the worker for the cleaning process makes it difficult to achieve an automatized painting process.
Various cleaning apparatus have been proposed for automatically cleaning paint spray guns. These proposed cleaning apparatus basically have a plurality of cleaning nozzles disposed in a casing. In operation, a paint spray gun to be cleaned is placed in the casing, and a solvent such as a thinner is ejected from the cleaning nozzles to blow or dissolve away a paint deposit on the nozzle of the paint spray gun.
The conventional cleaning apparatus are effective in cleaning a single paint spray gun as mounted on a robot apparatus or the like. However, they fail to clean a painting apparatus having plurality of paint spray guns within a short period of time. Therefore, the earlier cleaning apparatus are unable to accomplish an efficient process of painting automobile bodies.
The paint spray guns generally have a paint spray nozzle projecting toward a body. In a painting process, a relatively large amount of paint tends to remain attached to the boundary between the nozzle and the body and in the vicinity of the ejection hole of the nozzle. When such a paint spray gun with locally different amounts of paint deposited thereon is cleaned by the conventional cleaning apparatus, a considerable quantity of solvent should be ejected to the paint spray gun in order to completely remove the paint deposit at the boundary between the nozzle and the body and the paint deposit in the vicinity of the ejection hole of the nozzle. This is not economical since an excessive amount of solvent is applied to the body and other portions where the paint deposit is comparatively small in quantity.
In the cleaning apparatus of the type described above, a mist containing a large amount of thinner is likely to leak out between the casing and the paint spray gun being cleaned. Consequently, the thinner is scattered around in the working area and may be inhaled by the workers, thus causing a serious problem as to the health of the workers.
After a painting process is completed by the painting apparatus, the paint remains deposited in a pipe which supplies the paint to the paint spray gun. The paint in the pipe is solidified into a clog which may prevent paint from being supplied to the paint spray gun in a subsequent painting process. In automobile assembling plants, automobiles of different colors are assembled at the same time, and different paint coats are applied by the painting apparatus to different automobile bodies. When paint of one color is replaced with paint of another color in the painting apparatus, if a certain amount of the previous paint remains in the pipe connected to the spray gun after a painting process has been finished, the new paint mixes with the previous paint remaining in the pipe. This is highly disadvantageous in that paint of desired color cannot be coated on an automobile body.